The present invention relates to a device for sound transmission in a motor vehicle.
The propulsion motors of modern motor vehicles are very smooth-running internal combustion engines which generate operating noise that is hardly audible in the interior of the vehicle. Under some circumstances, the operating noise of the internal combustion engine is audible through the secondary noise of the turning wheels, a ventilation system that is turned on, etc. Under certain circumstances, it may be desirable to audibly transmit the operating noise of the driving engine into the interior of the vehicle.
Published European patent application no. EP 1,306,829 describes a device for transmitting the noise of an internal combustion engine in which a housing having a partition delimits or defines two separate subspaces. The partition is interrupted by a pivotable valve which separates the two subspaces. The first subspace is connected to the intake manifold of the internal combustion engine, while the second subspace leads to a wall of the vehicle or directly into the interior of the vehicle. In the first subspace, sound pressure vibrations in the intake manifold act on the half of the transmission valve which protrudes into that space and is thereby excited to execute a pivoting movement. In the second subspace, the vibrating pivoting movement of the transmission valve results in transmission of sound to the interior of the vehicle.
The subspace connected to the intake manifold may have a static mean pressure which differs from that of the subspace connected to the interior of the vehicle. To maintain this static pressure difference, a seal is maintained on the gap between the axis of rotation of the transmission valve and the edges of the adjacent partition. Therefore, the valve has on both sides an axially parallel web that is held with pressure between rubber gaskets of the partition to form a seal. The pressure in combination with the comparatively rigid sealing material prevents the transmission valve from pivoting freely. Resonance is attenuated. The potential of the arrangement described there is not fully utilized with regard to the efficiency that can be achieved in sound transmission.